Optical filter, method of manufacturing optical filter, optical filter unit, method of manufacturing optical filter unit, and optical measurement apparatus

Abstract

There is provided an optical filter having a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range. The optical filter includes a first optical function layer and a second optical function layer each having a transmittance that varies in a polarization direction of linearly polarized light at vertical incidence. The first optical function layer and the second optical function layer each have a high transmittance axis that is determined by a polarization direction in which transmittance of linearly polarized light at vertical incidence is greatest. The first optical function layer and the second optical function layer are disposed such that an angle formed by the high transmittance axis of the first optical function layer and the high transmittance axis of the second optical function layer is within a range of 90°±30°.

What is claimed is: 
     
         1 . An optical filter having a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range, the optical filter comprising:
 a first optical function layer and a second optical function layer each having a transmittance that varies in a polarization direction of linearly polarized light at vertical incidence, wherein:   the first optical function layer and the second optical function layer each have a high transmittance axis, the high transmittance axis being determined by a polarization direction in which transmittance of linearly polarized light at vertical incidence is greatest, and   the first optical function layer and the second optical function layer are disposed such that an angle formed by the high transmittance axis of the first optical function layer and the high transmittance axis of the second optical function layer is within a range of 90°±30°.   
     
     
         2 . The optical filter according to  claim 1 , further comprising a substrate that supports the first optical function layer and the second optical function layer, wherein:
 the first optical function layer is disposed on a surface side of the substrate, and   the second optical function layer is disposed on another surface side of the substrate.   
     
     
         3 . The optical filter according to  claim 1 , further comprising a substrate that supports the first optical function layer and the second optical function layer, wherein
 the first optical function layer and the second optical function layer are layered on either surface side of the substrate.   
     
     
         4 . The optical filter according to  claim 1 , wherein:
 the first optical function layer is a layer having a greater difference between a maximum transmittance and an average transmittance, and the second optical function layer is a layer having a smaller difference between a maximum transmittance and an average transmittance, and   the optical filter satisfies an Expression (1).   
       
         
           
             
               
                 
                   
                     
                       
                         ( 
                         
                           
                             T 
                             ⁢ 
                             2 
                             ⁢ 
                             max 
                           
                           - 
                           
                             T 
                             ⁢ 
                             2 
                             ⁢ 
                             ave 
                           
                         
                         ) 
                       
                       / 
                       
                         ( 
                         
                           
                             T 
                             ⁢ 
                             1 
                             ⁢ 
                             max 
                           
                           - 
                           
                             T 
                             ⁢ 
                             1 
                             ⁢ 
                             ave 
                           
                         
                         ) 
                       
                     
                     ≥ 
                     
                       1 
                       / 
                       2 
                     
                   
                 
                 
                   
                     Expression 
                     ⁢ 
                         
                     
                       ( 
                       1 
                       ) 
                     
                   
                 
               
             
           
         
         where T 1 max and T 1 ave represent the maximum transmittance and the average transmittance of the first optical function layer, respectively, and T 2 max and T 2 ave represent the maximum transmittance and the average transmittance of the second optical function layer, respectively. 
       
     
     
         5 . The optical filter according to  claim 1 , wherein the optical filter is a neutral density filter. 
     
     
         6 . The optical filter according to  claim 1 , wherein the optical filter is a wavelength filter. 
     
     
         7 . The optical filter according to  claim 1 , wherein the optical filter satisfies an Expression (2). 
       
         
           
             
               
                 
                   
                     
                       
                         ( 
                         
                           Tmin 
                           / 
                           Tmax 
                         
                         ) 
                       
                       × 
                       
                         100 
                         [ 
                         % 
                         ] 
                       
                     
                     ≥ 
                     
                       95 
                       [ 
                       % 
                       ] 
                     
                   
                 
                 
                   
                     Expression 
                     ⁢ 
                         
                     
                       ( 
                       2 
                       ) 
                     
                   
                 
               
             
           
         
         where Tmin and Tmax represent a minimum value and a maximum value of transmittance, respectively, when a polarization direction of linearly polarized light at vertical incidence is changed. 
       
     
     
         8 . An optical filter having a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range, the optical filter comprising:
 a first optical function layer and a second optical function layer having a reflectance that varies in a polarization direction of linearly polarized light at vertical incidence; and   a substrate that supports the first optical function layer and the second optical function layer,   wherein:
 the first optical function layer is disposed on a surface side of the substrate, 
 the second optical function layer is disposed on another surface side of the substrate, 
   the first optical function layer and the second optical function layer each have a high reflectance axis, the high reflectance axis being determined by a polarization direction in which reflectance of linearly polarized light at vertical incidence is greatest, and   the first optical function layer and the second optical function layer are disposed such that an angle formed by the high reflectance axis of the first optical function layer and the high reflectance axis of the second optical function layer is within a range of 90°±30°.   
     
     
         9 . A method of manufacturing the optical filter according to  claim 1 , the method comprising:
 forming the first optical function layer on a front surface of a substrate while moving the substrate in a specific direction with respect to a first target, the first target being a material of the first optical function layer;   inverting the substrate so that a back surface of the substrate faces a second target, the second target being a material of the second optical function layer, and rotating the substrate on a center of the substrate as a rotation center in the specific direction within a range of 90°±30°; and   forming the second optical function layer on the back surface of the substrate.   
     
     
         10 . A method of manufacturing the optical filter according to  claim 1 , the method comprising:
 forming the first optical function layer on a front surface of a substrate while moving the substrate in a specific direction with respect to a first target, the first target being a material of the first optical function layer;   rotating the substrate on a center of the substrate as a rotation center in the specific direction within a range of 90°±30°; and   forming the second optical function layer on the first optical function layer.   
     
     
         11 . A method of manufacturing an optical filter that includes a fifth optical function layer having a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range, the method comprising:
 forming the fifth optical function layer on a surface of a substrate while moving the substrate in a specific direction with respect to a target, the target being a material of the fifth optical function layer, and while rotating the substrate on a center of the substrate as a rotation center in the specific direction.   
     
     
         12 . An optical filter unit comprising a first optical filter and a second optical filter that have a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range, wherein:
 the first optical filter includes a first substrate and a first optical function layer supported by the first substrate, the first optical function layer having a transmittance that varies in a polarization direction of linearly polarized light at vertical incidence,   the second optical filter includes a second substrate and a second optical function layer supported by the second substrate, the second optical function layer having a transmittance that varies in a polarization direction of linearly polarized light at vertical incidence,   the first optical function layer and the second optical function layer each have a high transmittance axis, the high transmittance axis being determined by a polarization direction in which transmittance of linearly polarized light at vertical incidence is greatest, and   the first optical filter and the second optical filter are disposed such that an angle formed by the high transmittance axis of the first optical filter and the high transmittance axis of the second optical filter is within a range of 90°±30°.   
     
     
         13 . A method of manufacturing the optical filter unit according to  claim 12 , the method comprising:
 producing the first optical filter by forming the first optical function layer on a surface of the first substrate that moves in a specific direction with respect to a first target, the first target being a material of the first optical function layer;   producing the second optical filter by forming the second optical function layer on a surface of a second substrate that moves in a specific direction with respect to a second target, the second target being a material of the second optical function layer; and   disposing the first optical filter and the second optical filter such that an angle formed by the specific direction in which the first substrate moved and the specific direction in which the second substrate moved is within a range of 90°±30°.   
     
     
         14 . An optical measurement apparatus comprising the optical filter according to  claim 1 . 
     
     
         15 . An optical measurement apparatus comprising the optical filter unit according to  claim 12 . 
     
     
         16 . The optical measurement apparatus according to  claim 14 , comprising an insertion-removal device configured to insert or remove the optical filter into or from an optical path of light to be measured. 
     
     
         17 . The optical measurement apparatus according to  claim 15 , comprising an insertion-removal device configured to insert or remove the optical filter unit into or from an optical path of light to be measured. 
     
     
         18 . The optical measurement apparatus according to  claim 14 , configured to measure brightness or chromaticity of a measurement target. 
     
     
         19 . The optical measurement apparatus according to  claim 15 , configured to measure brightness or chromaticity of a measurement target.